The present invention relates to a screen printing apparatus and, more particularly, to a screen printing apparatus which has a roller carrying cleaning paper for removing residue, such as paste, attached on a surface of a screen mask and paste attached inside openings of the mask pattern, using the cleaning paper.
When film (pattern) forming is repetitively carried out on substrates by screen printing, paste begins to remain on the side of the mask surface which is in contact with the substrate or within the openings in the mask. Thereby, a blur or dimness gradually appears in the pattern printed on the substrate, which causes a pattern short-circuit or a pattern line-break. Therefore, it is necessary to perform a cleaning operation for removing the attached paste residue (mask cleaning) by cleaning the mask which has been used for a certain number of printings.
For such mask cleaning, for example, Japanese Patent Application Laid-Open No. 63-59535 proposes a cleaning apparatus for a printing machine in which a cleaning roller is arranged in contact with the lower surface of a printing plate, and the cleaning roller is vibrated in the direction of its shaft using compressed air or the like to wipe off ink attached onto the lower surface of the printing plate. Japanese Patent Application Laid-Open No. 5-229108 proposes a cleaning apparatus for a printing machine which operates to wipe the lower side of a mask using a roll cloth in combination with a suction nozzle.
Since the openings of a pattern or the amount of clearance between patterns has been getting smaller in recent high-definition masks, problems occur as described below.
In the vibration cleaning roller method described above, if residue transferred onto the roller surface is not removed from the roller when the apparatus is operated without human intervention for a long time, the residue may be retransferred onto the mask during the continuous operation. Therefore, it is necessary for the cleaning roller to be provided with an adhesive force by increasing the friction coefficient of the cleaning roller surface. However, the cleaning roller cannot be vibrated at a high speed if the cleaning roller surface is provided with a large friction coefficient, and, accordingly, the residue attached on the inside of openings cannot be completely removed in a high-definition mask.
On the other hand, in the method which uses a roll cloth in combination with a suction nozzle, the cleaning apparatus can be operated without human intervention for a long time because the mask is cleaned continuously with a new cloth. However, there occurs a problem in that, since the winding direction of the roll cloth is unidirectional in order to perform cleaning always with a new cloth surface, residue tends to remain on the edge of the narrow opening portion of the mask pattern, particularly on the winding direction side, and so the residue cannot be completely removed.